The aspects of the disclosed embodiment relate to the general field of the reflection of electromagnetic waves, particularly radio waves, and more particularly the field of preventing the effects of radio waves reflected by structures such as the facades of buildings on the space surrounding these structures. In particular, it concerns the effects of radio waves reflected by buildings located in airport zones on the proper operation of radio measurement systems.
In the context of the planning of airport zones, a major problem is that of determining the best way of siting the buildings required for the operation of the airport services, with the aim of minimizing the indirect effects of this siting on radio-sensitive areas. This is because these structures generally have large facades, which act as reflectors of the radio waves transmitted by the various transmission sources present in the vicinity of the airport zone or within this zone. In some cases, the reflection by the facade of a building of the radio transmission produced by a source which may or may not be distant from the building can prove extremely troublesome, insofar as the signal received by the facade is reflected toward an area where it will interfere with the radio transmissions taking place in this area. This is the case, in particular, if a building located in an area relatively close to a landing runway reflects toward the runway a radio transmission whose frequency band is located in the band occupied by transmissions of the landing system (ILS), particularly the band occupied by the “localizer” (providing radio alignment on the runway axis). This parasitic reflection, if strong enough, may affect the localizer signal and consequently disrupt the alignment of landing aircraft on the runway axis.
Because of the presence of numerous radio sources, notably the ILS antennas themselves, the problem of parasitic reflections from buildings is a major problem which is usually resolved by drawing up a siting plan including areas, notably those areas that are relatively close to the runways, where the location of any structure of significant size is prohibited. Taking into consideration, notably, the concentration of urban development and the desire to locate airport zones relatively close to urban areas, it becomes increasingly necessary to maximize the level of occupation of airport zones in terms of surface area. It is therefore more urgent than ever to find a solution to the problems of parasitic reflections of radio signals in sensitive directions.
According to the known prior art in this field, the facades of buildings which may accidentally give rise to parasitic reflections in sensitive directions may theoretically be equipped with patch structures, the purpose of which is to create, together with the wall on which they are installed, a diffraction device for reflecting incident waves, transmitted by external electromagnetic sources, in a preferred direction, which avoids the creation of interference in a sensitive area. A structure of this type is generally composed of conductive elongate structural elements arranged so as to form ribs spaced apart from each other. The ribs are generally tubular elements having a specified thickness such that a given value of phase shift is created between the wave directly reflected by the wall of the building and that reflected by the ribs. In this way, a diffraction grating of the Bragg grating type is formed, enabling the incident wave to be diffracted in a desired direction, according to the phase shift created by the ribs of the diffraction device.
According to the wavelength λ whose reflection in a given direction is to be prevented, the ribs forming the covering have a given thickness h, which may be relatively large if the wave in question has a frequency of the order of hundreds of megahertz. Because of their bulky nature, these elements are difficult to position on the surface of a facade, especially if the elements are installed after the construction of the building.
Furthermore, in order to ensure the correct diffraction of the incident wave, the facade exposed to the radiation whose effects are to be prevented is, in most cases, preferably equipped with ribs having a length substantially equal to the height of the facade, or occupying a significant portion of the upper of the facade. The fixing of the structural elements on the facade in question therefore creates a heavy load on the facade, attempts being made to minimize this load by using hollow tube-shaped structural elements. However, these elements are fragile objects, and suffer from the weakness of a lack of intrinsic rigidity.
Thus, the well-known types of prior art coverings use structural elements, the mounting of which on the facade to be equipped is relatively demanding in terms of their size, or more precisely their overall dimensions, and in terms of their weight, which is supported by the facade, and of the rigidity of the resulting structure.